Liquid crystal display having two or more spacings between electrodes

ABSTRACT

A liquid crystal display is described which includes a pair of transparent substrates disposed opposite each other sandwiching a liquid crystal layer therebetween, with a transparent electrode and an alignment film formed on the liquid crystal layer side of each of the substrates. The transparent electrodes disposed opposite each other in pairs are at two or more different spacings at least within one display area of a pixel.

This application is a division of application Ser. No. 08/816,806 filedMar. 19, 1997, now U.S. Pat. No. 5,872,611.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display that caneliminate viewing angle dependence.

2. Description of the Related Art

A liquid crystal display (LCD) includes a pair of substrates and aliquid crystal layer (liquid crystal cell) sandwiched between them, andproduces a display by altering the orientation of the liquid crystalmolecules in the liquid crystal layer and thereby changing the opticalrefractive index within the liquid crystal cell. Accordingly, the liquidcrystal molecules need to be aligned in an orderly manner within theliquid crystal cell.

One method commonly used to align the liquid crystal molecules in agiven direction involves forming an alignment film on the liquid crystallayer side of each substrate and controlling the substrate surfacecondition in such a manner as to interact with the liquid crystalmolecules. According to this method, a liquid crystal alignment filmmaterial is first applied on the facing surfaces of the pair ofsubstrates, and then dried and cured to form an alignment film on eachsurface, and preferential orientation is given by rubbing the surface ofthe alignment film with a nylon cloth or the like (rubbing method).

An inorganic alignment film or an organic alignment film may be used asthe alignment film for the above purpose. Oxides, organic silanes,metals, and metallic complexes are examples of the inorganic alignmentfilm materials. As the organic alignment film materials, polyimideresins are widely used; by rubbing the polyimide film surface formed onthe substrate the liquid crystal molecules can be aligned in a givendirection.

Of such liquid crystal displays, thin-film transistor (TFT) liquidcrystal displays (TFT-LCDs) are constructed using twisted nematic liquidcrystals. In the TN liquid crystal display, the liquid crystal moleculesare arranged with their long axes lying substantially parallel to thepair of substrates and gradually twisting through 90° between them; whena voltage is applied between electrode conductive lines formed on therespective substrates and an electric field is formed in a directionperpendicular to the substrates, the molecular alignment is altered withthe liquid crystal molecules being caused to line up in the direction ofthe electric field by virtue of the di-electric anisotropy of the liquidcrystal, thus producing a change on the optical refractive index withinthe liquid crystal layer.

In such a TN liquid crystal display, since the liquid crystal moleculeshave the property of refractive index anisotropy (birefringence), aphenomenon occurs in which the contrast varies depending on the angle atwhich the observer views the screen of the liquid crystal display. Thisphenomenon will be explained with reference to FIGS. 1, 2, and 3.

FIGS. 1 and 2 are a plan view and a perspective view, respectively, of atypical TN liquid crystal display, and FIG. 3 shows a cross sectiontaken along line F-F' in FIG. 1. The liquid crystal display is an activematrix display, and includes a pair of wiring substrates 131 and 132 anda liquid crystal layer 133 sandwiched between them. One wiring substrate131 consists of a glass substrate 111a, a transparent pixel electrode114, and an alignment film 116b, while the other wiring substrate 132consists of a glass substrate 111a, a transparent counter-electrode 115,and an alignment film 116b.

The edges of the two wiring substrates 131 and 132 are sealed with aresin or the like (not shown) in such a manner as to surround the liquidcrystal layer 133. Peripheral circuits for driving the liquid crystallayer 133, etc. are mounted outward of the sealing resin. Around thepixel electrode 114 are arranged scanning lines 112 and signal lines 113intersecting with each other. Electrical signals are applied to thescanning line 112 and signal line 113 connected to the pixel electrode114 to drive the liquid crystal layer through a TFT 120.

Liquid crystal molecules 133a in the liquid crystal layer 133 placedbetween the two wiring substrates 131 and 132 are oriented in such amanner that they twist through 900 between the two substrates 131 and132, the average orienting direction of the liquid crystal moleculesprojected on the substrate being substantially parallel to the directionof line F-F'. Also, the liquid crystal molecules 133a have a pretiltangle δ with respect to the substrates 131 and 132. This pretilt angle δis provided to prevent the occurrence of disclination lines due tomultidomain; because of the pretilt angle δ when a voltage is appliedbetween the pixel electrode 114 and the counter electrode 115, theliquid crystal molecules 133a line up uniformly in the direction of thepretilt angle δ. In FIG. 2, the arrow 134 indicates the rubbingdirection of the substrate 131 and the arrow 135 the rubbing directionof the substrate 132, while the arrow 136 indicates the positive viewingdirection. Such an arrangement is also employed in liquid crystaldisplays of other types than the active matrix.

In conventional liquid crystal displays, however, since the direction inwhich the liquid crystal molecules line up when an electric field isapplied is predetermined, a phenomenon occurs in which the contrastvaries depending on the angle at which the observer views the liquidcrystal display. The reason why this phenomenon occurs will be explainedwith reference to FIG. 4 showing the voltage-transmittance (V-T)characteristics of a normally white mode liquid crystal display whichproduces a white display when no voltage is applied. Here, when theliquid crystal molecules 133a are viewed from the θ1 side in FIG. 3, theviewing direction is said to be the positive viewing direction, and whenviewed from the θ2 side, it is said to be the negative viewingdirection.

When the liquid crystal display is viewed from directly above (from adirection perpendicular to the substrate plane), a V-T characteristicsuch as shown by solid line L1 in FIG. 4 is obtained. As can be seen, asthe applied voltage value increases, the light transmittance decreasesuntil it becomes substantially zero at a certain applied voltage value,at voltages above which the transmittance remains substantially zero.

On the other hand, the viewing angle is shifted from the direct-aboveposition toward the positive viewing direction (θ1 side in FIG. 3), aV-T characteristic such as shown by solid line L2 in FIG. 4 is obtained.As can be seen, the light transmittance decreases with increasingapplied voltage until the voltage reaches a particular value, from whichpoint the transmittance begins to increase and then gradually decreases.This means that at a particular angle of light incidence (viewing angle)the liquid crystal molecules are tilted in the same direction and therefractive index anisotropy of the liquid crystal molecules is lost,resulting in the loss of the optical rotatory power. That is, at aparticular viewing angle an inversion phenomenon (contrast reversal)occurs in which the dark and light parts of an image appear as light anddark, respectively.

Conversely, when the viewing angle is shifted toward the negativeviewing direction (θ2 side in FIG. 3), the refractive index of theliquid crystal molecules becomes difficult to change and the V-Tcharacteristic shown by solid line L3 in FIG. 4 is obtained, whichindicates that the light transmittance is hard to change. As a result,contrast between black and white drops markedly.

More specifically, when the applied voltage is zero or relatively low,the center molecule 133a appears as an ellipse to the observer 137positioned in the positive viewing direction, as shown in FIG. 5A. Whenthe applied voltage is gradually increased, the center molecule 133atilts toward the direction of the electric field and there is an instantin time at which the center molecule 133a appears as a true circle tothe observer 137, as shown in FIG. 5B. At this time, the lighttransmittance is the highest. When the applied voltage is furtherincreased, the center molecule 133a stands up substantially parallel tothe direction of the electric field, as shown in FIG. 5C, and againappears as an ellipse to the observer 137. In this manner, therefractive index (Δn) varies with the tilt angle of the liquid crystalmolecule; therefore as the viewing angle is shifted toward the positiveviewing direction θ1, the inversion phenomenon in which the dark andlight parts of an image appears reversed occurs at a particular angle.

In other viewing directions (the negative viewing direction) than thepositive viewing direction θ1, no inversion phenomenon occurs becausethe V-T characteristic is different, but for the same reason asdescribed above, there occurs a phenomenon in which the contrast ratiobetween black and white decreases with an increasing viewing angle.

In the TN liquid crystal display, the inversion phenomenon and decreasedcontrast as described above are very annoying to the observer, and makeone doubt the display characteristics of the liquid crystal display.

Various methods have heretofore been proposed to improve the viewingangle characteristic peculiar to such TN liquid crystal displays andenhance the display quality. For example, Japanese Laid-open PatentPublication No. 60-211424 and The Institute of Electronics, Informationand Communication Engineers, Technical Research Report ("ComplementaryTN (CTN)-TN with wide viewing angle -," pp. 35-41, Feb. 1993) disclosemethods in which each pixel is divided so that two or more differentmolecular orientations are provided. Furthermore, Japanese Laid-openPatent Publication No. 3-230120 ("Liquid Crystal Display" by SharpKabushiki Kaisha) proposes a method that uses a compensation plate,while Japanese Laid-open Patent Publication No. 1-200329 discloses amethod for improving the viewing angle characteristic by adjusting theliquid crystal materials and liquid crystal cell thickness.

The various methods proposed for improving the viewing anglecharacteristic of the liquid crystal display, however, have had thefollowing problems.

For example, the methods involving dividing every pixel and providingtwo or more different molecular orientations include, for example, amethod in which an alignment film formed from an organic film is etched,or selectively masked by photolithography, and then subjected to rubbingso that a masked region is made a nonoriented region and an unmaskedregion an oriented region, thus forming differently oriented regions,especially regions with opposite orientations, within the same pixelarea. According to this technique each pixel can be formed withorientations for both the positive and negative viewing directions, sothat the contrast decrease in the negative viewing direction can beprevented. However, in either method, foreign matter adheres to thealignment film or the alignment film is scratched, which may degrade thedisplay quality of the liquid crystal display.

On the other hand, with the method involving the use of a compensationplate, the viewing angle cannot be increased on the opposite side fromthe side for which the compensation plate is intended, while with themethod involving adjusting the liquid crystal materials and liquidcrystal cell thickness, it is difficult to improve the quality of theliquid crystal display since the materials that can be used are limited.

Another known method for preventing the inversion phenomenon andcontrast reduction is one disclosed in Japanese Laid-open PatentPublication No. 2-12. According to this method, which is used for anactive matrix liquid crystal display, a display electrode forming eachpixel is split into several parts and a capacitor is coupled to eachsplit display electrode, making it possible to create orientations inseveral different directions by forming different electric fields withinthe same pixel, thus achieving an improvement in the viewing anglecharacteristic. While this method of driving the split displayelectrodes is effective in improving the viewing angle characteristicresulting from changes in retardation such as observed on normally blackmode liquid crystal displays, little effect can be obtained inpreventing the half-tone (gray-scale) inversion phenomenon caused by thetilting of liquid crystal molecules. That is, this method is effectivein improving the viewing angle characteristic for normally black modeliquid crystal displays, but is not effective for normally white modeliquid crystal displays that provide good contrast.

Furthermore, all of the above-described methods have had the problem ofrequiring extra steps in the manufacture of liquid crystal displays,leading to increased manufacturing cost.

SUMMARY OF THE INVENTION

The liquid crystal display of this invention comprises a pair oftransparent substrates disposed opposite each other sandwiching a liquidcrystal layer therebetween, with a transparent electrode and analignment film formed on the liquid crystal layer side of each of saidsubstrates. Said transparent electrodes disposed opposite each other inpairs are at two or more different spacings at least within one displayarea of a pixel.

In one embodiment of the present invention, bumps and depressions areformed, using a transparent photosensitive resin, between saidtransparent substrates and said transparent electrodes to provide two ormore different spacings between said transparent electrodes.

In another embodiment of the present invention, bumps and depressionsare formed using an inorganic film between said transparent substratesand said transparent electrodes to provide two or more differentspacings between said transparent electrodes.

In still another embodiment of the present invention, a portion thatprovides two or more different spacings between said electrodes isformed extending over two or more pixels.

According to another aspect of the present invention, the liquid crystaldisplay comprises a pair of transparent substrates sandwiching a liquidcrystal layer therebetween, and a plurality of pixels with electrodesthereof provided on a side of each of said substrates that faces saidliquid crystal layer. A line-patterned insulating film is formed on atleast one of said substrates in such a manner as to cover at least apart of a region corresponding to each of said pixels between saidelectrodes and said liquid crystal layer, said line-patterned insulatingfilm being formed so that an average direction of direction taken over alongitudinal length of each individual line crosses substantially atright angles with an average direction of orienting directions of liquidcrystal molecules projected on said substrate.

In another embodiment of the present invention, a second line-patternedinsulating film made of the same material as said line-patternedinsulating film is formed between adjacent lines of said line-patternedinsulating film to a thickness smaller than a thickness of saidline-patterned insulating film.

In still another embodiment of the present invention, a thirdline-patterned insulating film made of a different material from saidline-patterned insulating film is formed between adjacent lines of saidline-patterned insulating film.

In still another embodiment of the present invention, said thirdline-patterned insulating film is formed from two or more line-patternedinsulating films of different materials.

In still another embodiment of the present invention, the angle that theaverage direction of directions taken over the longitudinal length ofeach individual line of said line-patterned insulating film makes withthe average direction of orienting directions of liquid crystalmolecules projected on said substrate, is 70° at minimum and 110° atmaximum.

In still another embodiment of the present invention, saidline-patterned insulating film is formed in a straight line pattern.

In still another embodiment of the present invention, saidline-patterned insulating film is formed in a wavy line pattern.

In still another embodiment of the present invention, at least one of aline width and a line spacing of said line-patterned insulating film issmaller than or equal to a spacing between said pair of substrates.

In still another embodiment of the present invention, each individualline of said line-patterned insulating film is formed with tapered filmwalls along both longitudinal sides thereof so that liquid crystalmolecules in a liquid crystal layer region on one of said longitudinalsides are oriented in a direction opposite from an orienting directionof liquid crystal molecules in a liquid crystal layer region on theother longitudinal side.

In still another embodiment of the present invention, a line width ofsaid line-patterned insulating film is 0.5 μm at minimum and 12 μm atmaximum and a line spacing of said line-patterned is larger than orequal to 0 μm but not larger than twice said line width.

In still another embodiment of the present invention, each of saidtapered film walls is formed at an angle of 1° at minimum and 45° atmaximum with respect to a surface of said substrate.

In still another embodiment of the present invention, said liquidcrystal molecules are provided with a pretilt angle not larger than 1°.

In still another embodiment of the present invention, saidline-patterned insulating film is formed on each of said two substratesin such a manner that a line pattern on one substrate is displacedwidthwise from a corresponding line pattern on the other substrate.

In still another embodiment of the present invention, adjacent lines ofsaid line-patterned insulating film are connected together at least onelongitudinal end thereof.

According to still another aspect of the present invention, the liquidcrystal display comprises a pair of wiring substrates disposed oppositeeach other sandwiching a liquid crystal layer therebetween, each of saidsubstrates having a plurality of electrodes formed on a liquid crystallayer side thereof, each pair of electrodes on said substrates forming apixel. One or more slit-like openings are formed per pixel in each ofsaid electrodes on at least one of said substrates, each of saidopenings extending longitudinally in a direction perpendicular to anaverage orienting direction of liquid crystal molecules projected onsaid substrate, and each region forming one pixel on one substrate ismade larger than a corresponding region forming one pixel on the othersubstrate by an arbitrary value in directions parallel to said averageorienting direction, said opposing electrodes being displaced relativeto each other in two directions parallel to said average orientingdirection.

In another embodiment of the present invention, said slit-like openingsare formed in said pixels on both of said substrates, said slit-likeopenings on one substrate being displaced from said slit-like openingson the other substrate in such a manner that said slit-like openings onsaid one substrate are positioned alternately between said slit-likeopenings on said other substrate along directions parallel to saidorienting direction.

In still another embodiment of the present invention, a width of each ofsaid slit-like openings is not smaller than a spacing between said pairof wiring substrates.

In still another embodiment of the present invention, said liquidcrystal molecules are provided with a pretilt angle of 0°.

According to still another aspect of the present invention, the liquidcrystal display comprises a pair of wiring substrates disposed oppositeeach other sandwiching a liquid crystal layer therebetween, each of saidsubstrates having a plurality of electrodes formed on a liquid crystallayer side thereof, each pair of opposing electrodes on said substratesforming a pixel. One or more line-patterned low-permittivity insulatingfilms are formed per pixel on each of said electrodes on at least one ofsaid substrates, each of said insulating films extending longitudinallyin a direction perpendicular to an average orienting direction of liquidcrystal molecules projected on said substrate, and each region formingone pixel on one substrate is made larger than a corresponding regionforming one pixel on the other substrate by an arbitrary value indirections parallel to said average orienting direction, said opposingelectrodes being displaced relative to each other in two directionsparallel to said average orienting direction.

In another embodiment of the present invention, said line-patternedlow-permittivity insulating films are formed between said liquid crystallayer and said pixels on both of said substrates, said insulating filmson one substrate being displaced from said insulating films on the othersubstrate in such a manner that openings on said one substrate arepositioned alternately between openings on said other substrate alongdirections parallel to said orienting direction.

In still another embodiment of the present invention, a width of each ofsaid line-patterned low-permittivity insulating films is not smallerthan a spacing between said pair of wiring substrates.

In still another embodiment of the present invention, each of saidline-patterned low-permittivity insulating films has tapered edges.

In still another embodiment of the present invention, said liquidcrystal molecules are provided with a pretilt angle of 0°.

According to still another aspect of the present invention, the liquidcrystal display comprises a pair of wiring electrodes disposed oppositeeach other sandwiching a liquid crystal layer therebetween, electrodesformed on a liquid crystal layer side of each of said substrates, and amatrix array of pixels each formed between a pair of opposing electrodeson said substrates. Each of said electrodes provided on one of saidpaired substrates and corresponding to one pixel is formed in acomb-like shape with teeth thereof extending substantially parallel toan average orienting direction of liquid crystal molecules projected onsaid substrate.

In another embodiment of the present invention, a spacing between saidteeth is not smaller than a spacing between said pair of wiringsubstrates.

According to still another aspect of the present invention, the liquidcrystal display comprises a pair of wiring electrodes disposed oppositeeach other sandwiching a liquid crystal layer therebetween, electrodesformed on a liquid crystal layer side of each of said substrates, and amatrix array of pixels each formed between a pair of opposing electrodeson said substrates. Each of said electrodes provided on one of saidpaired substrates and corresponding to one pixel is provided with one ormore open slits that are formed extending substantially parallel to anaverage orienting direction of liquid crystal molecules projected onsaid substrate.

In still another embodiment of the present invention, a width of each ofsaid slits is not smaller than a spacing between said pair of wiringsubstrates.

Thus, the invention described herein makes possible the advantages of(1) providing a liquid crystal display with improved viewing anglecharacteristic for all viewing directions without degrading the displayquality of the liquid crystal display and without imposing restrictionson the materials, construction, fabrication methods, etc., and (2)providing a liquid crystal display that achieves an improvement indisplay quality at low cost and that can be applied to normally whitemode display.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing an example of a conventional art liquidcrystal display.

FIG. 2 is a perspective view of the conventional art liquid crystaldisplay.

FIG. 3 is a cross-sectional view taken along line F-F' in FIG. 1.

FIG. 4 is a graph showing the applied voltage-transmittancecharacteristics (V-T characteristics) of the conventional art liquidcrystal display.

FIGS. 5A to 5C are schematic diagrams for explaining an inversionphenomenon that occurs in a liquid crystal display.

FIGS. 6A and 6B are graphs showing the applied voltage-transmittancecharacteristics (V-T characteristics) of a liquid crystal displayaccording to the present invention.

FIG. 7 is a schematic cross-sectional view of a liquid crystal displayaccording to Example 1 of the present invention.

FIGS. 8A and 8B are graphs showing the applied voltage-transmittancecharacteristics (V-T characteristics) of the liquid crystal display ofExample 1.

FIGS. 9A to 9C are schematic diagrams showing bump/depression patternsin the liquid crystal display of the present invention.

FIG. 10 is a plan view showing a portion of a liquid crystal displayaccording to Example 3 of the present invention.

FIG. 11 is a cross-sectional view of an active matrix substrate formingpart of the liquid crystal display of FIG. 10.

FIG. 12 is a plan view showing a portion of a liquid crystal displayaccording to Example 4 of the present invention.

FIG. 13 is a cross-sectional view showing a portion of a liquid crystaldisplay according to Example 5 of the present invention.

FIG. 14 is a cross-sectional view showing a portion of a liquid crystaldisplay according to Example 6 of the present invention.

FIG. 15 is a cross-sectional view showing a portion of a liquid crystaldisplay according to Example 7 of the present invention.

FIG. 16 is a cross-sectional view showing a portion of a liquid crystaldisplay according to Example 8 of the present invention.

FIG. 17 is a plan view showing a portion of a liquid crystal displayaccording to Example 9 of the present invention.

FIG. 18 is a cross-sectional view taken along line A-A' in FIG. 17.

FIG. 19 is a cross-sectional view of the liquid crystal display of thepresent invention in which a line-patterned insulating film is formedwith adjacent lines contacting each other.

FIG. 20 is a cross-sectional view of the liquid crystal display of thepresent invention, showing a line-patterned insulating film in analternative form wherein each film line is provided with tapered sides.

FIG. 21 is a cross-sectional view of the liquid crystal display of thepresent invention, showing a line-patterned insulating film in a furtheralternative form wherein each film line is provided with tapered sides.

FIG. 22 is a cross-sectional view of an active matrix liquid crystaldisplay according to Example 10 of the present invention.

FIG. 23 is a plan view of the liquid crystal display of FIG. 22.

FIG. 24 is a graph showing the applied voltage-transmittancecharacteristics (V-T characteristics) of the liquid crystal display ofExample 10 of the present invention.

FIG. 25 is a plan view of a liquid crystal display according to anotherexample of the present invention.

FIG. 26 is a plan view of a liquid crystal display according to anotherexample of the present invention.

FIG. 27 is a cross-sectional view of a liquid crystal display accordingto Example 11 of the present invention.

FIG. 28 is a cross-sectional view of a liquid crystal display accordingto another example of the present invention.

FIG. 29 is a plan view of a liquid crystal display according to anotherexample of the present invention.

FIG. 30 is a plan view of a liquid crystal display according to anotherexample of the present invention.

FIG. 31 is a plan view of a TN active matrix liquid crystal displayaccording to Example 12 of the present invention.

FIG. 32 is a cross-sectional view taken along line C-C' in FIG. 31.

FIG. 33 is an enlarged view of portion E in FIG. 31.

FIG. 34 is a graph showing the applied voltage-transmittancecharacteristics (V-T characteristics) of the liquid crystal display ofExample 12 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred examples of the present invention will be described below.

In one aspect of the invention, a pair of transparent electrodesdisposed opposite each other are at two or more different spacings atleast within a display area of one pixel (hereinafter simply calledpixel).

The threshold voltage at which the transmittance of a liquid crystallayer begins to change is a function of the electrode spacing, asexpressed by Equation (1) below. Therefore, with the electrode spacingvarying within the same pixel, the threshold voltage Vth varies in thevarious regions within the pixel. ##EQU1##

In Equation (1), d is the liquid crystal cell thickness (electrodespacing), Ec is the value of the threshold electric field at which theinitial molecular alignment in the liquid crystal begins to make atransition to a different molecular alignment, and k_(ij) is theelasticity of the liquid crystal material. The elasticity k_(ij)indicates k₁₁ (splay), k₂₂ (twist), or k₃₃ (bend) according to the kindof deformation, and k₁₁ (homogeneous molecular alignment) or k₁₁ + (k₃₃-2k₂₂)/4 according to the kind of initial molecular alignment.Furthermore, Δ.di-elect cons. is the dielectric anisotropy that theliquid crystal material has.

As can be seen from Equation (1), by varying the electrode spacing,various threshold values Vth can be obtained regardless of the liquidcrystal material used. Accordingly, it is possible to obtain various V-Tcurves within one pixel, as shown in FIG. 6A. As a result, when anobserver views the liquid crystal panel, these V-T curves appearcombined as shown in FIG. 6B, thus relaxing the inversion phenomenonthat occurs when the viewing angle is shifted toward the positiveviewing direction.

Since the regions that provide different electrode spacings can beformed in any position in an orderly manner within one pixel or acrosstwo or more pixels, the viewing angle characteristic when viewed fromany direction can be improved.

Examples according to the above aspect of the invention will now bedescribed in detail below with reference to relevant drawings.

EXAMPLE 1

FIG. 7 shows a cross section of a one-pixel area in a liquid crystalpanel of a liquid crystal display according to one example of theinvention. As illustrated, the liquid crystal panel includes atransparent glass substrate 1a, bumps 5 of various heights formedthereon, and a transparent electrode 2a formed over the bumps 5. On topof the transparent electrode 2a is formed an alignment film 3a which isprocessed for orientation. Furthermore, a transparent electrode 2b andan alignment film 3b are formed on top of a transparent substrate 1b,the alignment film 3b being processed for orientation. The substrates 1and 2 are placed opposite each other with a liquid crystal layer 6sandwiched between them.

The fabrication of this liquid crystal panel is performed in thefollowing sequence. First, an acrylic film is transferred onto thetransparent glass substrate 1a, to form the bumps 5 of various heights.The heights of the bumps 5 can be set at various values to provide thedesired electrode spacings. In the present example, the heights of thebumps are set to provide electrode spacings d1=10 μm, d11=8 μm, d12=5μm, and d13=3 μm.

Next, in the same manner as in the manufacture of conventional liquidcrystal panels, the transparent electrode 2a is formed by depositing anITO (indium tin oxide) transparent conductive film or the like. On topof the transparent electrode 2a, polyimide or like material is appliedto form the alignment film 3a which is then processed for orientation,thus completing the substrate 1.

In the same manner as above, the transparent electrode 2b and thealignment film 3b are formed on top of the glass substrate 1b, and thealignment film 3b is processed for orientation, to complete the othersubstrate 2.

Thereafter, the substrates 1 and 2 are placed facing each other so thatthe liquid crystal cell thickness is set at about 10 μm, and liquidcrystal molecules, plastic beads, etc. are sealed between them to formthe liquid crystal layer 6, thus completing the fabrication of theliquid crystal panel.

When a 30-Hz square wave voltage was gradually applied to this liquidcrystal panel and the liquid crystal panel was viewed from a position atan angle of 40° with respect to the positive viewing direction, a V-Tcharacteristic as shown in FIG. 8B was obtained and no inversionphenomenon was observed. This is because, of the presence of the bumps 5of different heights in each pixel, providing different thresholdvoltages Vth1, Vth11, Vth12, and Vth13 at positions with differentelectrode spacings d1, d11, d12, and d13. Thus, the apparent V-T curveis a combined form of the individual V-T curves, and as a result, a goodviewing angle characteristic free from inversion phenomenon can beobtained when viewed from any direction.

EXAMPLE 2

In this example, an inorganic film such as SiN was formed on thesubstrate 1a and etched to form the bumps 5. The resulting liquidcrystal panel showed a good viewing angle characteristic, as in Example1.

In the above examples, the bumps 5 of different heights were formedwithin each single pixel. Instead of forming an individual bump patternwithin each pixel as shown in FIG. 9A, a bump pattern extending over twoor more pixels may be formed as shown in FIG. 9B. It is also possible toform bumps on top of each bump pattern formed extending over two or morepixels, as shown in FIG. 9C. In FIGS. 9A to 9C, a square marked by athick solid line indicates one pixel.

Any of the above examples has dealt with a black and white duty panel,but it will be appreciated that the present invention can also beapplied to active matrix liquid crystal panels using switching devicessuch as TFTs and also to color liquid crystal panels using colorfilters.

As is apparent from the above description, in the present aspect of theinvention, various threshold voltages Vth can be obtained regardless ofthe liquid crystal material by varying the electrode spacing within eachpixel. Accordingly, it is possible to obtain various V-T curves withineach pixel; when the observer views the liquid crystal panel, these V-Tcurves appear combined together, and thus, the problems of inversionphenomenon in the positive viewing direction and contrast reduction inthe negative viewing direction can be alleviated. Furthermore, theregions that provide different electrode spacings can be formed in anypositions within one pixel or across two or more pixels, and thealignment films are free from scratches and foreign matter. As a result,the viewing angle characteristic when viewed from any direction can beimproved without imposing limitations on the structure or on thefabrication process.

In another aspect of the present invention, a line-patterned insulatingfilm is formed in such a manner that an average direction of directionstaken over the longitudinal length of each individual line crossessubstantially at right angles with an average direction of orientingdirections of the liquid crystal molecules projected on the substrate.As a result, when a voltage is applied to the liquid crystal layer, theangle at which the liquid crystal molecules in the portions of theliquid crystal layer where no line-patterned insulating film is formedare caused to line up is different from the angle at which the liquidcrystal molecules in the portions of the liquid crystal layer where theline-patterned insulating film is formed are caused to line up under thesame condition. The different angles at which the molecules are causedto line up result in different molecular alignments within the samepixel.

Such different molecular alignments can be obtained not only by formingthe insulating film in a line pattern but by varying the thickness orthe material.

Examples according this aspect of the invention will be described indetail below with reference to relevant drawings.

EXAMPLE 3

FIG. 10 is a plan view showing a portion of a TN active matrix liquidcrystal display embodying the present invention, and FIG. 11 is across-sectional view showing an active matrix substrate which forms partof the liquid crystal display. In this liquid crystal display, a liquidcrystal layer 33 is sealed between an active matrix substrate 31 and acounter substrate 32 disposed opposite each other. The active matrixsubstrate 31 includes a glass substrate 31a on which a transparentelectrode (pixel electrode) 31c, a line-patterned insulating film 31d,and an alignment film 31e are formed, while the counter substrate 32includes a glass substrate 32a on which a color filter 32b, atransparent electrode 32c, and an alignment film 32e are formed. Liquidcrystal molecules in the liquid crystal layer 33 are aligned in such amanner as to twist through 90° between the substrates 31 and 32. Theedges (not shown) of the substrates 31 and 32 are sealed with a resin orthe like, and peripheral circuits (not shown), etc. are mounted.

In the active matrix substrate 31, scanning lines 12 and signal lines 13are formed intersecting with each other on the insulating glasssubstrate 31a, as shown in FIG. 10. Near each intersection of thescanning lines 12 and signal lines 13 is formed a thin-film transistor(hereinafter referred to as the TFT) 20 that acts as a switching device.In the present example, the TFT 20 is an amorphous silicon TFT. The TFT20 may be formed on each scanning line 12.

Each TFT 20 is connected to one of a plurality of pixel electrodes 31cformed in a matrix array, and also connected electrically to onescanning line 12 and one signal line 13. The connection of the TFT 20 tothe scanning line 12 is accomplished by using a gate electrode 15 formedon the insulating substrate 31a and branching out from the scanning line12; the connection of the TFT 20 to the signal line 13 is accomplishedby using a source electrode 16 branching out from the signal line 13 andpartially extending over the gate electrode 15; and the connection ofthe TFT 20 to the pixel electrode 31c is accomplished by using a drainelectrode 17 a portion of which lies above the gate electrode 15.

The pixel electrode 31c is formed in such a manner as to overlap ascanning line 12 adjacent to the scanning line connected to the TFT 20.The overlapping portion forms a capacitor 18. Alternatively, acapacitance line may be formed separately from the scanning line 12 andthe capacitor 18 may be formed on the capacitance line.

A plurality of insulating film lines 31d are formed parallel to eachother on the pixel electrode 31c except where the capacitor 18 isformed. These insulating film lines 31d are provided to improve viewingangle dependence. The presence of the insulating film lines 31d alsoserves to prevent shorting due to the inclusion of foreign matter in theliquid crystal layer and stabilizes the TFT performance. The insulatingfilm lines 31d are formed by first depositing a silicon nitride film of600 nm thickness over the entire surface of the insulating substrate 31ausing a CVD process, for example, and then patterning the film in a linepattern. At this time, the insulating film lines 31d are formed in sucha manner that an average direction of directions taken over thelongitudinal length of each individual line crosses substantially atright angles with an average direction of orienting directions of theliquid crystal molecules projected on the substrate 31a, and preferablywithin the range of 90°±20°. Since the insulating film lines 31d can beformed in the same processing step of patterning an insulatingprotective film usually formed between the pixel electrode 31c and theliquid crystal layer 33, no extra fabrication steps are needed.

On the substrate 31a with the insulating film lines 31d is formed thealignment film 32e for controlling the orientation of the liquid crystalmolecules. The alignment film 32e is subjected to rubbing.

In the above-constructed liquid crystal display of the present example,the insulating film lines 31d are formed parallel to each other withtheir longitudinal sides extending generally in a direction crossingsubstantially at right angles with the average orienting direction ofthe liquid crystal molecules projected on the substrate. In thisstructure, when a voltage is applied between the pixel electrode 31c andthe transparent electrode 32c across the liquid crystal layer 33, asshown in FIG. 11, the strength of the electric field applied to theliquid crystal layer is different where no insulating film lines 31d areformed than where the insulating film lines 31d are formed. As a result,in those portions of the liquid crystal layer where no insulating filmlines 31d are formed, i.e., in each position corresponding to spacing bbetween the insulating film lines 31d, the liquid crystal molecules lineup, in response to the applied voltage, at a different angle (shown byan arrow) than the angle (shown by another arrow) at which the liquidcrystal molecules are caused to line up under the same condition inthose portions of the liquid crystal layer where the insulating filmlines 31d are formed, i.e., in each position corresponding to the linewidth a of each insulating film line 31d.

The different angles at which the molecules in the pixel are caused toline up result in different molecular alignments within the same pixel.In this situation, light incident obliquely (indicated by a large arrow)on the liquid crystal display passes through the liquid crystal layerregions with different molecular alignments, and therefore, the opticalrotatory power is not lost completely. This suppresses the inversionphenomenon of half-tone portions, and thus can improve viewing angledependence in a normally white mode liquid crystal display as well. Fromthe standpoint of improving the viewing angle dependence, it ispreferable that the insulating film lines 31d be formed with theirlongitudinal sides crossing at 90°±20° with the average orientingdirection of the liquid crystal molecules projected on the substrate.

Furthermore, when the line width a or line spacing b of theline-patterned insulating film 31d is made smaller than the thickness dof the liquid crystal layer 33, the viewing angle characteristic can beimproved, particularly for 20° and greater viewing angles where theinversion phenomenon of half-tone portions can occur most conspicuously.Preferably, the width a or the spacing b should be made less than d/2.7.

In this example, silicon nitride is used as the material of theinsulating film lines 31d, but this is only an example; other materialsmay be used such as inorganic insulating films formed of aluminum,tantalum or silicon oxides or their nitrides, or organic insulatingfilms formed of polyimide, polyamide, or polystyrene. The same appliesto the insulating protective film.

When an organic insulating film such as mentioned above is used, a filmof about 100 nm thickness is first formed by screen printing, forexample, and then patterned by photolithography or by photolysis usingdeep UV (wavelength 250 nm). The patterning can also be performed usinga printing process. Furthermore, such an organic insulating film canalso be used as the alignment film 31e.

EXAMPLE 4

In this example, a wavy-line-patterned insulating film is used insteadof the straight-line-patterned insulating film.

FIG. 12 is a plan view showing an active matrix substrate 31 on whichwavy insulating film lines 31d are formed. The same parts as those shownin FIG. 10 are designated by the same numerals. In this example also,the insulating film lines 31d are formed in such a manner that anaverage direction of directions taken along the longitudinal length ofeach individual film line, though it makes its way in zigzag directions,crosses substantially at right angles with an average direction oforienting directions of the liquid crystal molecules projected on thesubstrate 31a. By forming the insulating film lines 31d in this manner,viewing angle dependence can be eliminated, as in the case of Example 3.

In this example, the insulating film is formed in a wavy line pattern,but alternatively, it may be formed in a triangular wave pattern orother curved pattern.

EXAMPLE 5

In this example, each insulating film line is formed in a tapered shapesloping down on both longitudinal sides thereof.

Figure B is a cross-sectional view of a liquid crystal display accordingto this example. In this liquid crystal display, the insulating filmlines 31d are each formed in a tapered shape sloping down on bothlongitudinal sides thereof. The longitudinal sides of the insulatinglines 31d can be formed in a sloped shape by isotropic etching or by aphotoresist etchback technique.

In the structure of this example, by making the pretilt angle of theliquid crystal molecules smaller than the taper angle a of theassociated film side, the liquid crystal molecules on both tapered sidesof each film line can be provided with opposite tilt angles, as shown inFIG. 13, which serves to eliminate viewing angle dependence for both thepositive and negative viewing directions. On the other hand, when thepretilt angle of the liquid crystal molecules is made greater than thetaper angle α of the associated film side, the inversion phenomenon ofhalftone portions can be prevented, which serves to improves the viewingangle dependence of the liquid crystal display, as in the liquid crystaldisplay shown in FIG. 12.

The taper angle a should preferably be set within a range of 1° to 45°with respect to the substrate surface. With the taper angle a thus set,the liquid crystal molecules can be provided in a further reliablemanner with pretilt angles in both the normal and opposite directions,so that the viewing angle dependence in both the positive and negativeviewing directions can be eliminated efficiently.

Furthermore, the pretilt angle should preferably be set at 1° or less.In addition to setting the pretilt angle at 1° or less, the line width aand the line spacing b of the line-patterned insulating film 31d shouldpreferably be set at 0.5 μm ≦a ≦12 μm and 0<b≦2a, respectively. When theangle that the average longitudinal direction of the insulating filmlines 31d makes with the rubbing direction of the alignment film 31e forcontrolling the orientation of the liquid crystal molecules, is setwithin the range of 90°±20°, the elimination of the viewing angledependence can be further ensured.

EXAMPLE 6

This example is concerned with a structure in which a secondline-patterned insulating film of the same material is formed betweenthe insulating film lines.

FIG. 14 is a cross-sectional view of a liquid crystal display accordingto this example. In this example, insulating film lines 31f are eachformed in the portion corresponding to the spacing b in FIG. 11, thethickness of the insulating film lines 31f being smaller than that ofthe insulating lines 31d formed in the portions corresponding to theline width a. As a result, most of the substrate surface is covered withinsulating films of different thicknesses. The insulating film lines 31dare formed in such a manner that an average direction of directionstaken along the longitudinal length of each individual film line crossessubstantially at right angles with an average direction of orientingdirections of the liquid crystal molecules projected on the substrate31a. The insulating film lines 31f also are formed in like manner.

In the structure of this example, though the entire surface of thesubstrate is substantially covered with insulating films, the insulatingfilms lines 31f are formed thinner than the insulating films lines 31d;therefore, when a voltage is applied between the pixel electrode 31c andthe transparent electrode 32c across the liquid crystal layer 33, theresulting electric field is stronger through the insulating film lines31f than through the insulating film lines 31d. As a result, when avoltage is applied, the liquid crystal molecules above the portionscorresponding to the spacing b line up at a different angle (indicatedby an arrow) than the angle (indicated by another arrow) at which theliquid crystal molecules above the portions corresponding to the linewidth a are caused to line up under the same condition. This serves toeliminate viewing angle dependence.

In this example, the insulating film lines 31f are made thinner than theinsulating film lines 31d, but alternatively, the insulating film lines31f may be made thicker than the insulating film lines 31d. The pointhere is that the insulating films should be formed with differentthicknesses.

EXAMPLE 7

This example is concerned with a structure in which a thirdline-patterned insulating film of different material is formed betweenthe insulating film lines.

FIG. 15 is a cross-sectional view of a liquid crystal display accordingto this example. In this liquid crystal display, insulating film lines31g are formed in the portions corresponding to the spacing b in FIG.11, the material of the insulating film lines 31g being different fromthat of the insulating film lines 31d formed in the portionscorresponding to the line width a. More specifically, silicon nitrideand tantalum oxide having different relative permittivities, forexample, are used for the insulating films 31g and 31d, respectively.The insulating film lines 31d are formed in such a manner that anaverage direction of directions taken along the longitudinal length ofeach individual film line crosses substantially at right angles with anaverage direction of orienting directions of the liquid crystalmolecules projected on the substrate 31a. The insulating film lines 31galso are formed in like manner.

In the structure of this example, though the entire surface of thesubstrate is substantially covered with insulating films, the insulatingfilm lines 31g have a higher relative permittivity than the insulatingfilm lines 31d; therefore, when a voltage is applied between the pixelelectrode 31c and the transparent electrode 32c across the liquidcrystal layer 33, the resulting electric field is stronger through theinsulating film lines 31g than through the insulating film lines 31d. Asa result, when a voltage is applied, the liquid crystal molecules abovethe portions corresponding to the spacing b line up at a different angle(indicated by an arrow) than the angle (indicated by another arrow) atwhich the liquid crystal molecules above the portions corresponding tothe line width a are caused to line up under the same condition. Thisserves to eliminate viewing angle dependence.

In this example, the insulating film lines 31g are formed to provide ahigher relative permittivity than the insulating film lines 31d, but thepresent invention is not limited to this arrangement. Conversely, theinsulating film lines 31g may be formed to provide a lower relativepermittivity than the insulating film lines 31d, or other characteristicthan relative permittivity may be used to differentiate one type ofinsulting film from the other. The point here is that the two types ofinsulating film should be formed so that different electric fieldstrengths can be obtained.

Furthermore, in this example, one insulating film line 31g is formedbetween adjacent insulating film lines 31d, but alternatively, two ormore insulating film lines 31g having different relative permittivity orother characteristic may be formed between them.

EXAMPLE 8

In this example, line-patterned insulating films are formed on bothsubstrates disposed with the liquid crystal layer sandwiched betweenthem, and the line pattern formed on one substrate is displacedwidthwise from that formed on the other substrate.

FIG. 16 is a cross-sectional view of a liquid crystal display accordingto this example. In this liquid crystal display, a line-patternedinsulating film 31d is formed on the active matrix substrate 31, and aline-patterned insulating film 32d is formed on the counter substrate32, the line-patterned insulating films 31d and 32d being displaced inposition from each other in the width direction thereof. Theline-patterned insulating films 31d and 32d are each formed in such amanner that an average direction of directions taken along thelongitudinal length of each individual film line crosses substantiallyat right angles with an average direction of orienting directions of theliquid crystal molecules projected on the substrate 31a.

In the structure of this example, three different regions are formed: aregion where the portion corresponding to the spacing b of theline-patterned insulating film 31d is opposite the portion correspondingto the spacing b' of the line-patterned insulating film 32d; a regionwhere the portion corresponding to the spacing b or the spacing b' isopposite the insulating film line 31d or 32d; and a region where theinsulating film line 31d is opposite the insulating film line 32d. Thisstructure therefore offers the same effect as can be obtained when theline width or line spacing of the line-patterned insulating film 31d isreduced.

EXAMPLE 9

This example is concerned with a structure in which the insulating filmlines are connected together at both ends thereof.

FIG. 17 is a plan view of a liquid crystal display according to thisexample, and FIG. 18 is a cross-sectional view taken along line A-A' inFIG. 17. In FIGS. 17 and 18, the same parts as those shown in FIGS. 10and 11 are designated by the same reference numerals. In this liquidcrystal display, first an insulating film 20 is formed to cover most ofthe display area surface where the pixel electrodes 31c are formed in amatrix array on the active matrix substrate 31, and then, linelikeopenings 21 are etched into the insulating film 20 over selected regionsof the pixel electrode 31c, which results in the formation of insulatingfilm lines 31d. Adjacent insulating film lines 31d are connectedtogether at both ends thereof.

In this structure, the regions where the line openings 21 are formedcorrespond to the spacing b shown in FIG. 11, and the insulating filmregions where no line openings 21 are formed correspond to the linewidth a. The structure therefore provides a similar effect to thatobtained in Example 3. Furthermore, since each insulating film line isformed in a tapered shape, a similar effect to that obtained in Example5 can also be obtained. The insulating film lines 31d are formed in sucha manner that the longitudinal direction thereof makes an angle 90°±20°with the rubbing direction indicated by an arrow 11.

In Example 9 also, the same modifications as described in Examples 4 to8 can be made, in which case the same effects as mentioned in therespective examples can be obtained for the respective modifications.

In Example 9, adjacent insulating film lines 31d are connected togetherat both ends thereof, but the invention is not limited to theillustrated structure. In an alternative structure, each insulating filmline 31d may be connected to an adjacent film line at one end thereof.In this case, the insulating film lines 31d may be connected together,with each connecting end positioned in alternating fashion or in arandom order.

In Examples 3, 4, 5, and 9, no insulating film is formed betweenadjacent insulating film lines 31d, but the invention is not limited tosuch a structure. For example, the insulating film lines 31d may beformed in a tapered shape in such a manner that adjacent insulating filmlines contact with each other, as shown in FIG. 19. In such a structurealso, a stronger electric field is formed across the thinner regions ofthe insulating film 31d than across the thicker regions thereof.

In Examples 5 and 9, the taper-structured line-patterned insulating film31d does not have a planar top, but it will be recognized that theinsulating film 31d may be formed in such a manner that each film linehas a planar top as shown in FIG. 20. Also, the taper structure of theinsulating film line 31d includes a structure in which both sides of thetop are rounded as shown in FIG. 21. In this rounded taper structure,the angle that the average slope of the tangents to each rounded portionmakes with the substrate surface correspond to the taper angle. Thetaper angle should be set within the range of 1° to 45°.

In any of Examples 3 to 9, description has been given by taking anactive matrix liquid crystal display as an example, but it will beappreciated that the invention is also applicable to other types ofdisplay structure where nonlinear electric elements are not formed onone substrate, that is, simple matrix liquid crystal displays.

As is apparent from the above explanation, according to the above aspectof the invention, an insulating film is patterned in a line pattern, orinsulating films of different materials or different thicknesses areformed over the electrode in each pixel area. As a result, differentregions with different electric field strengths and therefore differentorientations can be formed within one pixel area. This structureprevents the inversion phenomenon occurring in the positive viewingdirection and the contrast degradation occurring in the negative viewingdirection, and thus improves the viewing angle dependence. Furthermore,since the inversion phenomenon of halftone portions can be suppressed,this structure can also be applied to normally white mode liquid crystaldisplays which provide good contrast. Moreover, since the step offorming the line-patterned insulating film can be performedsimultaneously with the patterning of the insulating protective filmformed between the electrode and the liquid crystal layer, no extrafabrication steps are needed. The invention thus provides a low-cost,high-contrast, and high-quality liquid crystal display.

In a further aspect of the present invention, of the pair of wiringsubstrates disposed opposite each other, at least one substrate has oneor more slit-like openings or low-permittivity insulating film linesformed in or on the electrode of each pixel. Such slit-like openings andlow-permittivity insulating film lines are formed in such a manner thatthe longitudinal direction thereof is perpendicular to the averageorienting direction of the liquid crystal molecules projected on thesubstrate; furthermore, each pixel region of the electrode formed on onesubstrate is made larger than the corresponding region of the electrodeformed on the other substrate by an arbitrary value in directionssubstantially parallel to the average orienting direction of the liquidcrystal molecules projected on the substrate. As a result, the electroderegions formed opposite each other are displaced from each other alongtwo directions parallel to the average orienting direction of the liquidcrystal molecules projected on the substrate, so that an obliquelyacting electric field is formed between the electrodes. When the pretiltangle of the liquid crystal molecules is set at 0°, the liquid crystalmolecules line up parallel to the obliquely acting electric field, andtherefore, it is easy to control the molecular alignment.

Because of the physical displacement between the opposing electroderegions, different regions where the liquid crystal molecules are causedto line up differently can be formed within the same pixel. Thisstructure greatly improves the viewing angle characteristic.

It is desirable that the width of the slit-like opening orlow-permittivity insulating film line be made larger than the spacingbetween the pair of wiring substrate, since a smaller width would makethe application of an oblique electric field to the liquid crystalmolecules difficult.

The step of forming the slit-like openings and the step of forming theabove-mentioned region of the electrode on the one substrate larger thanthe corresponding region of the electrode on the other substrate can beperformed simultaneously with the usual electrode patterning steps.Also, the step of forming the low-permittivity insulating film lines canbe performed simultaneously with the step of forming the insulatingprotective film formed to prevent shorting between the wiring substrate.Subsequent formation and rubbing processing of the organic alignmentfilms can be performed using a conventional processing step. Therefore,no extra processing steps are needed, and there is no possibility ofcontaminating the organic alignment films.

Examples according to the above aspect of the invention will bedescribed in detail below with reference to relevant drawings.

EXAMPLE 10

FIG. 22 shows a cross-sectional view of a TN active matrix liquidcrystal display according to Example 10. In this liquid crystal display,wiring substrates 61 and 62 with a plurality of electrode conductorsformed thereon are disposed opposite each other with a liquid crystallayer 63 sealed between them.

FIG. 23 shows a plan view of the wiring substrate 61. The wiringsubstrate 61 includes an insulating substrate 41a formed from glass orlike material, and scanning lines 42 and signal lines 43 formed thereonintersecting with each other. A pixel electrode 44 is formed in eachregion surrounded by the scanning lines 42 and signal lines 43. In onecorner of each of the regions is formed a switching device 50 which iselectrically connected to the pixel electrode 44 and also to onescanning line 42 and one signal line 43 adjacent to the pixel electrode44. A device of any desired structure can be used as the switchingdevice 50. In this example, an amorphous silicon thin-film transistor(hereinafter called the TFT) 50 is used.

On the other wiring substrate 62, there are formed a light blocking film(not shown) for blocking light to other regions than the pixel region,and a counter electrode 45.

In the counter electrode 45, there is formed, as shown by dotted linesin FIG. 23, a slit-like opening 48 extending perpendicular to theaverage orientating direction of the liquid crystal molecules projectedon the substrate. The average orienting direction here refers to thedirection in which the liquid crystal molecule in the center of theliquid crystal layer 63 is oriented. As shown in FIG. 22, each squareregion of the counter electrode 45, which forms one pixel region, ismade larger than the corresponding region of the pixel electrode 44along directions parallel to the average orienting direction of theliquid crystal molecules projected on the substrate. In this example,the width of the slit-like opening 48 is chosen to be about 10 μm. It isdesirable that this width be made larger than the spacing (about 5 μm)between the wiring substrates 61 and 62, since a smaller width wouldmake the application of oblique electric field components to the liquidcrystal molecules difficult. The slit-like opening 48 is formed at thesame time when the counter electrode 45 is patterned.

Furthermore, alignment films 46a and 46b for controlling the orientationof the liquid crystal molecules are formed on the wiring substrates 61and 62, respectively. The alignment films 46a and 46b, each formed froman organic material, are subjected to rubbing processing. The wiringsubstrates 61 and 62 are then bonded together, and liquid crystalmaterial is sealed in between the two substrates 61 and 62 (liquidcrystal cell), to form the liquid crystal layer 63. The pretilt angle ofthe liquid crystal molecules is 0°. The ends (not shown) of thesubstrates 61 and 62 are sealed with a resin or the like, and peripheralcircuits (not shown), etc. are mounted to complete the liquid crystaldisplay.

In this liquid crystal display, since the slit-like opening 48 is formedin the counter electode 45, an oblique electric field is formed betweenthe pixel electrode 44 and the counter electrode 45, as shown in FIG.22, so that the liquid crystal molecules can be aligned in thedirections shown by the arrows. Thus, within the same pixel region,different regions are formed where the liquid crystal molecules arecaused to line up in opposite directions; as a result, the V-Tcharacteristics shown in FIG. 24 can be obtained and the viewing anglecharacteristic of the liquid crystal display can be improved.

In Example 10, the slit-like opening 48 is formed in the counterelectrode 45. Alternatively, as sown in FIG. 25, slit-like openings 48(shown by solid lines in FIG. 25) may be formed in the pixel electrode44 on the wiring substrate 61 and slit-like openings 48 (shown by dottedlines in FIG. 25) in the counter electrode 45 on the wiring substrate 62in such a manner that the slit-like openings on one substrate arepositioned alternately between the slit-like openings on the othersubstrate along a direction parallel to the average orienting directionof the liquid crystal molecules projected on the substrate. Further, asshown in FIG. 26, slit-like openings 48 (shown by dotted lines in FIG.26) may be formed in the counter electrode 45 in such a manner that eachopening partially, for example, half faces an edge portion of the pixelelectrode 44 on the wiring substrate 61. On the other hand, when theslit-like openings 48 are formed in the pixel electrode 44, one end ofeach slit-like opening may be open, in which case the pixel electrode 44is formed in a comb-like or bellows-like shape.

Since the slit-like openings 48 may result in the formation ofdisclination lines due to disturbed orientation of the liquid crystalmolecules, a light blocking film may be formed over the openings toconceal such lines. Such light blocking film can be formed at the sametime when a light blocking film material is applied and patterned on thewiring substrate 62. The light blocking film can also be formed at thesame time when an opaque film, such as a titanium, tantalum, or aluminumfilm, for forming the switching device 50 is patterned on the wiringsubstrate 61, or when the scanning lines 42 are patterned using a wiringmaterial. In the case of the slit-like openings 48 shown in FIG. 26also, disclination lines formed at the boundaries between the differentregions where the liquid crystal molecules line up differently can beconcealed by forming light blocking film in the same manner as describedabove.

Any of the slit-like openings 48 shown in FIGS. 23, 25, and 26 canprovide similar effects. The more regions each pixel is divided into,the more natural the effect looks to the eye of the observer, but thisin turn reduces the ratio of aperture of the liquid crystal display.Therefore, it is desirable that the pixel be divided into an optimumnumber of regions according to the size of the pixel. For example, whenthe pixel size is about 70 μm×230 μm, it is desirable that the pixel bedivided into two to four regions.

In Example 10, an insulating protective film (not shown) may be formedon the pixel electrode 44 or the counter electrode 45 or on both, toprevent shorting between the wiring substrates 61 and 62. Thisinsulating protective film should preferably be formed with a windowopened in at least one portion thereof to prevent the dc component ofthe electric field from being applied to the liquid crystal molecules inthe pixel. With respect to the window-opened structure, JapaneseLaid-open Patent Publication No. 2-171721 and U.S. Pat. No. 5,066,110.are referred to in this application. Furthermore, color filters (notshown) may be provided on the wiring substrate 62 to achieve a colordisplay.

EXAMPLE 11

FIG. 27 shows a cross-sectional view of a liquid crystal displayaccording to Example 11. In this liquid crystal display, there isformed, in a convenient position between the counter electrode 45 andthe liquid crystal layer 63, a low-permittivity insulating film 47, asshown by dotted lines in FIG. 23, which extends in a directionperpendicular to the average orienting direction of the liquid crystalmolecules projected on the substrate. As shown in FIG. 27, the squareregion of the counter electrode 45 that forms one pixel is made largerthan the pixel electrode 44 in directions parallel to the averageorienting direction of the liquid crystal molecules projected on thesubstrate. It is desirable that the width of this insulating film 47 bemade larger than the spacing (about 5 μm) between the substrates, sincea smaller width would make the application of oblique electric fieldcomponents to the liquid crystal molecules difficult. The insulatingfilm 47 is made of silicon oxide or silicon nitride and formedsimultaneously with an insulating protective film (not shown) formed toprevent shorting between the wiring substrates 61 and 62. In otherrespects, the construction can be made identical to that of Example 10.

In this liquid crystal display, the low-permittivity insulating filmformed between the counter electrode 45 and the liquid crystal layer 63serves to weaken the electric field applied to the liquid crystal layer63 in that portion. As a result, as in Example 10, an oblique electricfield is formed between the electrodes, and the aligning direction ofthe liquid crystal molecules can be controlled as shown by the arrows.Since the liquid crystal molecules can be caused to line up in oppositedirections within one pixel, as in Example 10, the viewing anglecharacteristic of the liquid crystal display can be improved.

In Example 11, the low-permittivity insulating film 47 is formed betweenthe counter electrode 45 and the liquid crystal layer 63, but this maybe formed between the pixel electrode 44 and the liquid crystal layer 63(as shown by solid lines in FIG. 25) as well as between the counterelectrode 45 and the liquid crystal layer 63 (as shown by dotted linesin FIG. 25) in such a manner that one alternates with another, as shownin FIG. 26, along a direction parallel to the average orientingdirection of the liquid crystal molecules projected on the substrate.Alternatively, insulating film lines 47 (shown by dotted lines in FIG.26) formed between the counter electrode 45 and the liquid crystal layer63 may be arranged so that each film line partially, for example, halffaces an edge portion of the pixel electrode 44 on the wiring substrate61. Furthermore, the insulating film 47 may be formed continuouslyacross two or more pixels instead of being formed like a separate islandin each pixel. Moreover, if the insulating film is formed with taperededges as shown in FIG. 28, the aligning direction of the liquid crystalmolecules can be further stabilized.

As in Example 10, a light blocking film may be formed over thelow-permittivity insulating film 47 to conceal the disclination linesresulting from disturbed orientation of the liquid crystal molecules.

Any of the variation of the low-permittivity insulating film 47 shown inFIGS. 23, 25, and 26 can provide similar effects. The more regions eachpixel is divided into, the more natural the effect looks to the eye ofthe observer, but this in turn reduces the ratio of aperture of theliquid crystal display. Therefore, it is desirable that the pixel bedivided into an optimum number of regions according to the size of thepixel. For example, when the pixel size is about 70 μm×230 μm, it isdesirable that the pixel be divided into two to four regions.

Furthermore, color filters (not shown) may be provided on the wiringsubstrate 62 to achieve a color display.

The liquid crystal display of the present invention may be provided withboth the slit-like openings 48 shown in Example 10 and thelow-permittivity insulating film 47 shown in Example 11 in or on eachelectrode on at least one of the substrates.

In Examples 10 and 11, the invention is applied to an activematrix-driven liquid crystal display, but it will be appreciated thatthe invention is also applicable to a duty-driven liquid crystaldisplay. In the latter case, a slit-like opening 48a may be formed inthe pixel 45a formed on one wiring substrate 62, as shown in FIGS. 29and 30, wherein the electrodes 44a formed on the wiring substrate 61 areindicated by solid lines and the electrodes 45a formed on the wiringsubstrate 62 are shown by dotted lines. In the liquid crystal displaysshown in FIGS. 29 and 30, instead of the slit-like openings 48a alow-permittivity insulating film may be formed in a similar pattern.

As is apparent from the above description, according to the invention,since the liquid crystal molecules in the display can be easilycontrolled so that they line up in different directions, more than oneviewing directions can be built into each pixel. This structure servesto reduce the viewing angle dependence of the liquid crystal display.

The step of forming the slit-like opening in the pixel and the step offorming the low-permittivity insulating film between the pixel and theliquid crystal layer can be performed simultaneously with the usualpixel patterning step and protective insulating film forming step,respectively. This achieves low-cost production of liquid crystaldisplays having good display quality and high reliability.

In a still further aspect of the present invention, of a pair ofelectrodes provided on the pair of opposing wiring substrates to form apixel, at least one electrode is formed in a comb-like shape or with oneor more open slits. In this structure, an obliquely acting electricfield is formed in regions where no electrode is formed, and a forcehaving components acting parallel to the substrate is exerted on theliquid crystal molecules. Furthermore, since the electrode is formed insuch a manner that the teeth of the comb or the longitudinal sides ofthe slits extend substantially parallel to the average orientingdirection of the liquid crystal molecules, the liquid crystal moleculesare caused to line up in opposite directions on both outward sides ofeach tooth or on both inward side of each slit.

Since the liquid crystal molecules are thus caused to line up indifferent directions within each pixel, the inversion phenomenon thatoccurs in the positive viewing direction can be suppressed. In thenegative viewing direction also, since the liquid crystal moleculespartially stand up by the force having components acting parallel to thesubstrate, the refractive index of the liquid crystal molecules iscaused to change and the contrast can be improved.

Furthermore, if the teeth spacing or the slit width is made larger thanthe spacing between the two substrates, a situation that would occurwith a narrower spacing or width can be prevented where obliquecomponents of the electric field are difficult to be applied to theliquid crystal molecules.

The step of forming each pixel in a comb-like shape or with a slit orslits can be performed simultaneously with the usual pixel patterningstep without affecting the subsequent steps and without requiring extrasteps.

An example according to the above mode of the invention will bedescribed in detail below with reference to relevant drawings.

EXAMPLE 12

FIG. 31 is a plan view of a TN active matrix liquid crystal displayembodying the present invention. FIG. 32 is a cross-sectional view takenalong line C-C' in FIG. 31. In this liquid crystal display, a liquidcrystal layer 93 is sealed between wiring substrates 91 and 92 disposedopposite each other. The wiring substrate 91 includes an insulatingsubstrate 71a made of glass or like material, on which scanning lines 72and signal lines 73 are formed intersecting with each other. A pixelelectrode 74 is formed in each region surrounded by the scanning lines72 and signal lines 73. A switching device 80 is formed in one corner ofeach pixel region, and is electrically connected to the associated pixelelectrode 74 and also to the scanning line 72 and signal line 73adjacent to the pixel electrode 74. A device of any desired structurecan be used as the switching device 80. In this example, an amorphoussilicon thin-film transistor (hereinafter called the TFT) 80 is used.The pixel electrode 74 is formed in a comb-like shape as shown in FIG.31, with the teeth 74a of the comb extending parallel to the averageorienting direction (line D-D') of the liquid crystal moleculesprojected on the liquid crystal molecules.

On the other wiring substrate 92, a light blocking film (not shown) forblocking light to other regions than the pixel region, and a counterelectrode 75 are formed in this order from the side of the substrate 92.

Furthermore, alignment films 76a and 76b for controlling the orientationof the liquid crystal molecules are formed on the wiring substrates 91and 92, respectively, and are subjected to rubbing processing. Thewiring substrates 91 and 92 are then bonded together with the alignmentfilms 76a and 76b facing inside, and liquid crystals are sealed betweenthe two substrates 91 and 92, to form the liquid crystal layer 93. Theedges (not shown) of the substrates 91 and 92 are sealed with a resin orthe like, and peripheral circuits (not shown), etc. are mounted.

In this liquid crystal display, since the pixel electrode 74 is formedin a comb-like shape, as described above, an obliquely acting electricfield (electric lines of force are indicated by dotted lines) is formedin regions on both outward sides of each tooth 74a and between the pixelelectrode 74 and the counter electrode 75, and a force having componentsparallel to the substrate is exerted on the liquid crystal molecules.Furthermore, since the teeth 74a are formed extending parallel to theaverage orienting direction of the liquid crystal molecules projected onthe substrate, the liquid crystal molecules are caused to line up indirections toward the electrode in such a manner as to respond to thechange of the electric lines of force, as shown in FIG. 33 (an enlargedview of portion E in FIG. 31), the molecular alignment thus beingchanged in opposite directions on both outward sides of each tooth 74a.This results in the formation of different regions within the same pixelwhere the liquid crystal molecules are caused to line up in oppositedirections; consequently, the inversion phenomenon that occurs in thepositive viewing direction can be suppressed, as shown by solid line L2in FIG. 34. The teeth 74a need not necessarily be oriented exactly inparallel to the average orienting direction of the liquid crystalmolecules projected on the substrate, but may be displaced somewhat fromthe parallel direction.

In the negative viewing direction, on the other hand, since the liquidcrystal molecules partially stand up by the force having componentsacting parallel to the substrate, the refractive index of the liquidcrystal molecules is caused to change as shown by solid line L3 in FIG.34, providing an improvement in contrast.

The teeth 74a can be formed with a desired width and in any number, thewidth and number being chosen appropriately according to the liquidcrystal display. However, since an excessively narrow spacing betweenadjacent teeth 74a would make the application of oblique electric fieldcomponents to the liquid crystal molecules difficult, it is desirablethat the spacing between adjacent teeth 74a be made larger than thespacing (thickness of the liquid crystal layer 93) d between the wiringsubstrates 91 and 92. In this example, since the spacing d is about 5μm, the width of each tooth 74a is set at 10 μm and the spacing betweenadjacent teeth 74a also at 10 μm.

In the above example, the pixel electrode 74 is formed in a comb-likeshape, but the invention is not limited to this structure. Instead, oneor more open slits may be formed in the pixel electrode 74. In thiscase, it is desirable that each slit be formed with its longitudinalside extending substantially parallel to the average orienting directionof the liquid crystal molecules projected on the substrate, so that themolecular alignment is changed in opposite directions on both inwardsides of each slit, thus forming different regions within the same pixelwhere the liquid crystal molecules are caused to line up in oppositedirections. This structure provides the same effect as obtained when thepixel electrode 74 is formed in a comb-like shape. For the same reasonas described above, it is desirable that the slit width be made largerthan the spacing (thickness of the liquid crystal layer 93) d betweenthe wiring substrates 91 and 92.

In the above example, the pixel electrode 74 is formed in a comb-likeshape or with one or more slits, but the present invention is notlimited to forming the pixel electrode 74 in such structure. Instead,the counter electrode 75 may be formed in such structure.

The step of forming each pixel in a comb-like shape or with a slit-likeopening, as described above, can be performed simultaneously with theusual pixel patterning step. Accordingly, liquid crystal displays havinggood display quality and high reliability can be produced at low cost.

Furthermore, in the above example, an insulating protective film (notshown) may be formed on the pixel electrode 74 or the counter electrode75 or on both, to prevent shorting between the wiring substrates 91 and92. This insulating protective film should preferably be formed with awindow opened in at least one portion thereof to prevent the dccomponent of the electric field from being applied to the liquid crystalmolecules in the pixel. Furthermore, color filters (not shown) may beprovided on the wiring substrate 92 to achieve a color display.

In the above example, the invention is applied to a TN active matrixliquid crystal display, but the invention is not limited to thisapplication but can be applied to liquid crystal displays of othermodes. Furthermore, the invention is not limited to active matrix-drivendisplays but can also be applied to duty-driven liquid crystal displays,etc.

As is apparent from the above description, according to the presentinvention, since liquid crystal molecules can be caused to line up indifferent directions within the same pixel, the inversion phenomenonthat occurs in the positive viewing direction can be suppressed.Furthermore, since the liquid crystal molecules partially stand up bythe force having components parallel to the substrate, the contrast inthe negative viewing direction can be improved. Improvement in theviewing angle characteristic of the liquid crystal display is thusachieved.

The step of forming each pixel in a comb-like shape or with a slit-likeopening can be performed simultaneously with the usual pixel patterningstep. Accordingly, liquid crystal displays having good display qualityand high reliability can be produced at low cost.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A liquid crystal display comprising a pair oftransparent substrates sandwiching a liquid crystal layer therebetween,and a plurality of pixels with electrodes thereof provided on a side ofeach of said substrates that faces said liquid crystal layer, wherein aline-patterned insulating film is formed on at least one of saidsubstrates in such a manner as to cover at least a part of a regioncorresponding to each of said pixels between said electrodes and saidliquid crystal layer, said line-patterned insulating film being formedso that an average direction of directions taken over a longitudinallength of each individual line crosses substantially at right angleswith an average direction of orienting directions of liquid crystalmolecules projected on said substrate.
 2. A liquid crystal displayaccording to claim 1, wherein a second line-patterned insulating filmmade of the same material as said line-patterned insulating film isformed between adjacent lines of said line-patterned insulating film toa thickness smaller than a thickness of said line-patterned insulatingfilm.
 3. A liquid crystal display according to claim 1, wherein a thirdline-patterned insulating film made of a different material from saidline-patterned insulating film is formed between adjacent lines of saidline-patterned insulating film.
 4. A liquid crystal display according toclaim 3, wherein said third line-patterned insulating film is formedfrom two or more line-patterned insulating films of different materials.5. A liquid crystal display according to claim 1, wherein the angle thatthe average direction of directions taken over the longitudinal lengthof each individual line of said line-patterned insulating film makeswith the average direction of orienting directions of liquid crystalmolecules projected on said substrate, is 70° at minimum and 110° atmaximum.
 6. A liquid crystal display according to claim 1, wherein saidline-patterned insulating film is formed in a straight line pattern. 7.A liquid crystal display according to claim 1, wherein saidline-patterned insulating film is formed in a wavy line pattern.
 8. Aliquid crystal display according to claim 1, wherein at least one of aline width and a line spacing of said line-patterned insulating film issmaller than or equal to a spacing between said pair of substrates.
 9. Aliquid crystal display according to claim 1, wherein each individualline of said line-patterned insulating film is formed with tapered filmwalls along both longitudinal sides thereof so that liquid crystalmolecules in a liquid crystal layer region on one of said longitudinalsides are oriented in a direction opposite from an orienting directionof liquid crystal molecules in a liquid crystal layer region on theother longitudinal side.
 10. A liquid crystal display according to claim9, wherein a line width of said line-patterned insulating film is 0.5 μmat minimum and 12 μm at maximum and a line spacing of saidline-patterned is larger than or equal to 0 μm but not larger than twicesaid line width.
 11. A liquid crystal display according to claim 9,wherein each of said tapered film walls is formed at an angle of 1° atminimum and 45° at maximum with respect to a surface of said substrate.12. A liquid crystal display according to claim 1, wherein said liquidcrystal molecules are provided with a pretilt angle not larger than 1.13. A liquid crystal display according to claim 1, wherein saidline-patterned insulating film is formed on each of said two substratesin such a manner that a line pattern on one substrate is displacedwidthwise from a corresponding line pattern on the other substrate. 14.A liquid crystal display according to claim 1, wherein adjacent lines ofsaid line-patterned insulating film are connected together at, at least,one longitudinal end thereof.
 15. A liquid crystal display comprising apair of wiring substrates disposed opposite each other sandwiching aliquid crystal layer therebetween, each of said substrates having aplurality of electrodes formed on a liquid crystal layer side thereof,each pair of opposing electrodes on said substrates forming a pixel,wherein one or more line-patterned low-permittivity insulating films areformed per pixel on each of said electrodes on at least one of saidsubstrates, each of said insulating films extending longitudinally in adirection perpendicular to an average orienting direction of liquidcrystal molecules projected on said substrate, and each region formingone pixel on one substrate is made larger than a corresponding regionforming one pixel on the other substrate by an arbitrary value indirections parallel to said average orienting direction, said opposingelectrodes being displaced relative to each other in two directionsparallel to said average orienting direction.
 16. A liquid crystaldisplay according to claim 17, wherein said line-patternedlow-permittivity insulating films are formed between said liquid crystallayer and said pixels on both of said substrates, said insulating filmson one substrate being displaced from said insulating films on the othersubstrate in such a manner that openings on said one substrate arepositioned alternately between openings on said other substrate alongdirections parallel to said orienting direction.
 17. A liquid crystaldisplay according to claim 17, wherein a width of each of saidline-patterned low-permittivity insulating films is not smaller than aspacing between said pair of wiring substrates.
 18. A liquid crystaldisplay according to claim 17, wherein each of said line-patternedlow-permittivity insulating films has tapered edges.
 19. A liquidcrystal display according to claim 14, wherein said liquid crystalmolecules are provided with a pretilt angle of 0°.